1. Field
Exemplary embodiments of the present disclosure describe an article comprising a unidirectional heterojunction transistor, that is, a nitride semiconductor device, and a method of manufacturing the same, and more particularly, a unidirectional heterojunction transistor and a method of manufacturing the same, which can prevent a reverse leakage current using a rectification electrode.
Exemplary embodiments of the present disclosure also describe an article comprising a nitride semiconductor device including a mixed junction drain using Schottky contact and ohmic contact and a method of manufacturing the same.
2. Discussion of the Background
With the recent development of information communication technology, there may be a need for a transistor having a high-speed switching operation which is suitable for ultra high-speed and high-capacity signal transmission and a high voltage-resistant transistor suitable for a high-voltage environment, such as a hybrid vehicle, in various fields. However, conventional silicon-based transistors or GaAs-based transistors may have difficulties in complying with the need due to the limit of the materials themselves.
In contrast, a nitride-based transistor, in particular, a GaN-based may be suitable for ultra high-speed signal processing because it enables a high-speed switching operation as compared with a conventional silicon transistor, and it may be suitable for a high-voltage environment due to a high voltage-resistant characteristic of the materials themselves.
A nitride-based transistor, for example, a High Electron Mobility Transistor (HEMT) or a Heterostructure FET (HFET) using a heterojunction structure may be suitable for high-speed signal transmission due to high electron mobility because an electric current flows using Two-Dimensional Electron Gas (2DEG) generated at the interface between heterogeneous materials.
In a common GaN-based transistor, current flows in both directions by bringing a source electrode and a drain electrode into ohmic contact with each other. That is, current flows in both directions, that is, from the source electrode to the drain electrode and from the drain electrode to the source electrode.
In conventional application circuits that require a unidirectional electrification characteristic, in order to prevent current from flowing in a reverse direction, an additional diode may be combined with the drain electrode. Furthermore, in a conventional GaN-based transistor, current may be made to flow in one direction by combining Schottky contact diode with the drain electrode instead of an additional diode.
An example of a conventional nitride-based semiconductor device using a Schottky electrode is disclosed in Korean Patent Application Publication No. 10-2012-0064180, as shown in FIG. 1. In the disclosed nitride-based semiconductor device, in order to obtain a unidirectional electrification characteristic, a source electrode 133 is formed through ohmic contact with a barrier layer 124, and a gate electrode and a drain electrode 134 are formed through a Schottky contact with a Schottky electrode 136 or the drain electrode 134 is formed on the barrier layer 124 by mixing Schottky contact and ohmic contact. In the conventional nitride-based semiconductor device having such a structure, a forward current from the drain electrode 134 to the source electrode 133 is electrified, and a reverse current from the source electrode 133 to the drain electrode 134 is blocked.
If the drain electrode is used as Schottky contact, however, the conventional nitride-based semiconductor device may have a problem in that a threshold voltage generated due to a Schottky barrier becomes the threshold voltage of a forward state of a transistor irrespective of control of a gate threshold voltage.
Furthermore, in the conventional nitride-based semiconductor device, the threshold voltage may remain in the forward direction because the drain electrode is used by mixing Schottky contact and ohmic contact, but the prevention of a reverse leakage current may be limited because the reverse leakage current is generated through a drain region that is subject to ohmic contact in Two-dimensional Electron Gas (2DEG) that is formed by the junction of a channel layer and the barrier layer.